The invention relates to dynamic loudspeakers and in particular to the problem of increasing the rated steady power at which they can be driven.
The performance of loudspeakers can be numerically described by a variety of measurable characteristics. Besides magnetic characteristics, the ones most often considered are the peak power at which the speaker can be driven, the natural resonant frequency of the speaker, the frequency range of the speaker, the operating power of the speaker, the sensitivity of the speaker, the frequency-dependence of the gain and phase of the speaker, and the nominal steady power at which the speaker can be driven. The latter signifies the input power at which the speaker can be steadily driven without undergoing permanent damage.
With dynamic loudspeakers, the nominal steady power at which the speaker can be driven is limited by a number of factors, including the heat generated by the moving-coil unit of the speaker during operation. For this reason, high-powered moving-coil units are often comprised of moving coils wound on aluminum coil carriers and fabricated using highly-temperature resistant cement or glue. The moving coil principally transmit the heat which it generates to the central pole core and outer pole plates of the permanent magnet structure of the moving-coil unit, resulting in a heating-up of the entire magnet system. Contributing to this heat build-up is the fact that the magnet system of the moving-coil unit, for acoustical reasons, is often surrounded with mineral wool having heat-insulating characteristics. In some speakers, use is made of spider structures made of aluminum, a material of high thermal conductivity. However, the aluminum spider structures do not establish a heat-dissipating action. Typically, they are comprised of narrow radial arms leading to the front side of the speaker housing, with little or no transmission of heat from these spider arms to the housing. Most often, the ends of the spider arms are mounted on the spider housing by means of resilient material of extremely low thermal conductivity.